Novel Syntheses of Silica-Gold Core-Shell Particles

Methods for the synthesis of silica-gold core-shell particles presented in literature are not considered commercially viable due to various requirements: high reaction temperatures, the use of light-sensitive reagents, the use of ex-situ gold seeding adding to the number of time-consuming steps required in the syntheses. We have developed two novel syntheses that eliminate these issues. Syntheses first require the formation and capping of silica spheres with (3-mercaptopropyl)-trimethoxysilane (MPTMS) to functionalise the silica surfaces with sulfur to facilitate the binding of gold. The first method involves only these MPTMS capped silica spheres and the reduction of tetrachloroaurate at slightly elevated temperatures. This method involves very few steps and only two reagents, but does not allow for much control over the growth and seeding of the gold shells, which leads to the formation of thick gold shells. The second method involves these MPTMS capped silica spheres and the reduction of tetrachloroaurate at lower temperatures with external reducing agents hydroxylamine and NaBH4, to control the seeding and growth of the gold shells. This method involves more steps and reagents, but allows for more control over the resulting thinner gold shells. The resulting particles display surface plasmon resonance and dichroic optical properties.